No Oven Cleaner, either!

Turpentine or Mineral Spirits, on an old under-shirt rag, will clean off old grease, dirt, mold and grime. It may also soften up old Finish (varnish/shellac/?).

I have stripped stubborn varnish and Birchwood Casey "Lin-Speed" coatings with a small 1x2 inch square pad of green 'Scotch-Brite', saturated with Formby's stripper, following the grain & using very light pressure.

Change 'pads' as they load up with junk. Follow-up with several hand-rubbed coats of 50/50 mix of Linseed Oil & Turpentine.

I like a final coat and 'rag-buff' of Howard's "Wax & Feed".

Note some will disagree and say I'm a "Barbarian".

Approach has a lot to do with the 'Wood Situation' you start with.

(Here's photos of an abused 'trapdoor' I cleaned up):

I strip old, grungy stocks with MEK and 4-0 steel wool. Gets all the gunk and crap off the stock right down to the bare wood. This is followed by an application of boiled linseed oil and hand rubbed for that nice, low sheen look that we all like.
Jon